As the science world mourns we collected some of the Professor's most profound comments.

Black holes

Professor Hawking rose to fame after he discovered the phenomenon known as Hawking radiation, where black holes leak energy and fade to nothing.

Professor Hawking aspired to bring complex hypothesis a little bit closer to the public by using analogues such as Niagara Falls and spaghetti.

"A black hole has a boundary, called the event horizon. It is where gravity is just strong enough to drag light back, and prevent it escaping," he said.

"Because nothing can travel faster than light, everything else will get dragged back also. Falling through the event horizon, is a bit like going over Niagara Falls in a canoe.

"If you are above the falls, you can get away if you paddle fast enough, but once you are over the edge, you are lost. There's no way back. As you get nearer the falls, the current gets faster.

"This means it pulls harder on the front of the canoe, than the back. There's a danger that the canoe will be pulled apart. It is the same with black holes.

"If you fall towards a black hole feet first, gravity will pull harder on your feet than your head, because they are nearer the black hole.

"The result is, you will be stretched out longwise, and squashed in sideways. If the black hole has a mass of a few times our sun, you would be torn apart, and made into spaghetti, before you reached the horizon.

"However, if you fell into a much larger black hole, with a mass of a million times the Sun, you would reach the horizon without difficulty. So, if you want to explore the inside of a black hole, choose a big one."

The theory of everything

It was perhaps Professor Hawking's "theory of everything" that put him on the world arena.

He argued the universe evolved according to well-defined laws that explain how it all began.

"This complete set of laws can give us the answers to questions like, 'how did the universe begin?'," he said.

"Where is it going and will it have an end? If so, how will it end? If we find the answers to these questions, we really shall know the mind of God.

"Even if the universe does come to an end, it won't be for at least 20 billion years," he said.

Religion and God

Later, the self-confessed atheist explained what he meant when he said we might one day "know the mind of God".

With science providing answers to more and more questions, the notion of God has become redundant, he said.

"Before we understand science, it is natural to believe that God created the universe. But now science offers a more convincing explanation," he said.

"What I meant by 'we would know the mind of God' is, we would know everything that God would know, if there were a God, which there isn't. I'm an atheist.

"In my opinion, there is no aspect of reality beyond the reach of the human mind."

As for heaven and afterlife — also not possible, said Professor Hawking.

"I believe the simplest explanation is, there is no God. No-one created the universe and no-one directs our fate. This leads me to a profound realisation that there probably is no heaven and no afterlife either," he said.

"We have this one life to appreciate the grand design of the universe and for that, I am extremely grateful."

Aliens, space travel and AI

There is no God, but life on other planets is not such an alien concept, Professor Hawking revealed.

He said it was completely rational to assume there was intelligent life elsewhere; but if they visit, it may not turn out so well for us.

"The idea that we are alone in the universe seems to me completely implausible and arrogant," he said.

"Considering the number of planets and stars that we know exist, it's extremely unlikely that we are the only form of evolved life.

"If aliens ever visit us, I think the outcome would be much as when Christopher Columbus first landed in America, which didn't turn out very well for the Native Americans.

"I believe that life on Earth is at an ever-increasing risk of being wiped out by a disaster such as sudden nuclear war, a genetically engineered virus, or other dangers," he said.

"I think the human race has no future if it doesn't go into space."

We should pursue space travel, he said, but leave robots alone.

"Success in creating artificial intelligence would be the biggest event in human history. Unfortunately, it might also be the last," he said.

"Artificial intelligence could be a real danger in the not-too-distant future. It could design improvements to itself and out-smart us all."

Parallel universe

Professor Hawking suggested there could be multiple universes, not just the one we live in.

Again, to popularise science and plant the seed of knowledge, he once explained the possibility of parallel universes to teenagers by using British pop icon Zayn Malik's departure from boy group One Direction.

"My advice to any heartbroken young girl is to pay close attention to the study of theoretical physics. Because one day there may well be proof of multiple universes," he said.

"It would not be beyond the realms of possibility that somewhere outside of our own universe lies another different universe — and in that universe, Zayn is still in One Direction."

Imaginary time

But despite all efforts to draw trivial analogues to complex matters, there still remains one thing the world doesn't understand about his work — "imaginary time".

British comedian John Oliver once quipped: "If there is one thing you want people to understand about your work — bearing in mind that most people will never understand anything about your work — what would that be?"

Hawking replied: "Imaginary time. People think it's something you have in dreams or when you're up against a deadline. But it's a well-defined concept.

"Imaginary time is like another direction in space. It's the one bit of my work science fiction writers haven't used because they don't understand it."

Donald Trump

The brilliant mind of Professor Hawking also weighed in on political issues.

Asked if the theoretical physicist could explain United States President Donald Trump's meteoric ascendance to power, he said "I can't".

"He is a demagogue who seems to appeal to the lowest common denominator," he said.

Motor neurone disease

At the age of 21, Professor Hawking was diagnosed with a motor neurone disease and doctors gave him two years to live.

"Although I cannot move and I have to speak through a computer, in my mind I am free," he said.

"My disabilities have not been a significant handicap in my field, which is theoretical physics.

"Indeed, they have helped me in a way by shielding me from lecturing and administrative work that I would otherwise have been involved in.

His incredible life was made into a 2014 film A Theory of Everything.

Professor Hawking, who approved Eddie Redmayne's portrayal of him, said the film was "surprisingly honest".

"It was as close as I'll ever get to travelling back in time," he said.